Diamond bits employing natural or synthetic diamonds positioned on the face of a drill shank and bonded to the shank in a matrix of a secondary abrasive, such as tungsten carbide, by means of a metal bond, are well known in the art.
There are two general types: One in which the diamonds usually of very small gage are randomly distributed in the matrix; another type contains diamonds, usually of larger size, positioned in the surface of the drill shank in a predetermined pattern referred to as surface set. (See U.S. Pat. Nos. 3,709,308; 3,825,083; 3,871,840; 3,757,878; and 3,757,879.)
Drill bits formed according to the above procedure are subject to damage when used as bore-hole drill bits. Such damage results from localized destruction of the diamond matrix complex. When this occurs, the useful life of the bit may be terminated and extensive repairs or salvage of the bit is required by separating the diamonds and tungsten carbide from the steel shank.
In a copending application by some of us, Ser. No. 704,424, is described an earth boring diamond bit in which instead of using individual diamond particles distributed either in random orientation in a secondary abrasive matrix, such as tungsten carbide with a metallic bonding agent, or as surface set bits, cutter preforms are employed. The cutter preform may be made as described in U.S. Pat. No. 3,745,623 or by molding mixtures of diamond particles, secondary abrasive particles, and particles of a metallic bonding agent employing the techniques of the above patents in suitable shaped molds, for example, as described in U.S. Pat. 3,745,623 or by the hot press methods described in Pats. 3,841,852 and 3,871,840.